Ovens are devices typically equipped with a cooking room, a heating device for applying heat to the cooking room, and a circulation fan for circulating the heat produced by the heating device inside the cooking room to cook food. The ovens are cooking appliances to cook food by sealing up and heating the material, and the ovens may be generally classified by their heat sources into electric, gas, and microwave ovens. The electric oven uses an electric heater as a heat source, and the gas and microwave ovens use heat from gas and frictional heat of water molecules at high frequencies as heat sources, respectively. It is often the case that the user occasionally checks the cooking process to check out the status or add in some spices, and whenever that happens, the user is bothered to go to the oven and look in through the transparent window or open the oven door to check inside. It is also bothersome to have to check the cooking state while the user is cooking other dishes or receiving guests.